1. Field of the Invention
The present invention is directed to an apparatus and process to generate a foam under controlled conditions, measure its viscosity and facilitate measurements of its physical properties. In particular, the present invention is directed to a foam generator and viscometer apparatus and a process which is capable of controlling multiple variables during the generation of a foam and allowing the foam to flow under controlled conditions in order to maintain constant foam properties while being measured.
2. Prior Art
A number of industries, such as the petroleum drilling and production industry use foams for a wide range of tasks. For example, foams are utilized in the petroleum industry for: drilling underbalanced wells, the transport of proppants during fracturing of wells to improve production, to enhance oil recovery from partially depleted reservoirs, and for environmental remediation of underground water. In the case of drilling new wells into low-pressure reservoirs, conventional drilling muds are too heavy and can over-pressurize the porous rock formations and cause xe2x80x9cskin damagexe2x80x9d that reduces the flow of either crude and/or gas from the well. This problem is avoided by using lighter weight drilling fluids such as foams.
In petroleum applications, foam is produced on-site at a drilling and/or production location. The various components of the foam such as liquids and gases are mixed together and then pumped downhole. Accordingly, it is important to know the properties of the foam and to control its characteristics.
Additional applications would be in the chemical and pharmaceutical industries.
A study of foam properties includes measurements of its viscous properties and its physical properties such as foam texture, which includes bubble size, size distribution, and bubble shape. All instrument that can produce foam under controlled conditions and measure its properties will provide valuable engineering data that can be used in a variety of industries.
There have been proposals in the past to study foams and similar liquids. The Bass Patents (U.S. Pat. Nos. 5,306,734 and 5,394,738) disclose a device to study emulsions which includes a fixed volume mixing chamber and conventional flow meters to measure feed rates of oil and water into the mixing chamber. Bass measures viscosity of samples of the emulsion at ambient temperature and atmospheric pressure.
Joseph (U.S. Pat. No. 5,301,541) discloses a device and a method for drag determination having a rib surface 20 attached to an inner block 14 and a rib surface 22 attached to a housing 12.
There remains a need for an instrument and a process to generate a foam and measure its physical and viscous properties. The device should be capable of controlling a number of variables independently, such as foam quality (ratio of gas to total fluid volume), pressure, temperature, surfactants and other additives, bubble size and surface roughness.
The present invention produces a liquid-gas-surfactant foam by selectively mixing components of various ratios and controlling the resulting bubble size by adjusting the amount of mixing or shear energy applied. It also conveys the foam, at constant pressure and temperature, through a viscometer, and enables optical measurements of the foam""s physical properties.
Gas, contained under pressure in a cylinder, is dispensed and delivered through fluid lines. Liquids, including surfactants and additives, are initially premixed in a volume-calibrated container and then introduced via a pump into a mixing cell. Once the desired volume of liquids has been delivered into the mixing cell, pressurized gas is then allowed to flow into the mixing cell, thereby adding a volume of gas to the liquid volume. As the combined volume of liquid and gas increases inside the mixing cell, a piston begins to rise from its resting place upon a stop or stops.
Generation of foam is initiated by rotating a propeller driven by a shaft that is rotated by a variable speed motor. Flow within the mixing cell is forced upward in the center of the mixing chamber and thereafter is diverted downward along the sides of the mixing cell by a specially contoured piston.
Additional mixing of the foam can be achieved by optionally drawing liquids, gas and foam from either the top or bottom of the mixing cell with a pump and circulating back to the opposite end of the mixing cell.
After a satisfactory foam has been generated, valves may be manipulated to direct gas pressure to the top of the piston, thereby forcing a smooth continuous flow of foam from the mixing cell through a viscometer. The rate at which foam flows from the mixing cell may be measured by a linear voltage differential transformer. Foam from the mixing cell enters a fluid line and passes into a Couette-type viscometer having interchangeable elements (stationary cup and a rotor or a rotating sleeve and a stationary bob) with different values of surface roughness. This feature enables studies of the effects of surface roughness on xe2x80x9cwall slipxe2x80x9d of foams at a solid surface. Fluid flow is controlled by a metering valve located downstream of the viscometer that allows flow rate to be controlled by varying the opening of the valve. The physical properties of a foam may be visually and electronically assessed at four view ports. Two are located near the Generator, and two others are located on the entry and exit sides of the Viscometer.